Magnetron tube



D. GLASER MAGNETRON TUBE May 1, 1962 Filed Aug. 3l, 1959 IN VHV TOR.

DA V/D @SER BY Z z 5;

A TTORNE Y States an g Filed Aug. 31, 1959, Ser. No. 837,195

6 Claims. (Cl. 315-8) This invention relates to magnetron-type electron discharge tubes and to improvements in the construction of arent such tubes, particularly in the magnet used with such tubes.

One form of magnetron tube, to which the principles of the invention apply, includes an electrode assembly which comprises an elongated central cathode and a plurality of groups of elongated electrodes surrounding the cathode and secured together at their opposite ends by means of insulating end disks or plates. All of the electrodes are substantially parallel to each other. A cylindrical magnet surrounds the electrode assembly. In operation of this type of tube, a beam of current ows from the central cathode to one of the groups of electrodes at a time and this beam may be switched from one group of electrodes to the next.

One problem encountered with tubes of this type results from the fact that a considerable amount of magnetic ux ows out of the magnet and away from t-he tube as well as into the tube. The result is that two magnetron tubes cannot be operated in close proximity to each other without some precautions being taken to prevent this stray leakage from one tube from adversely aiecting the operation of theother.

Thus, the principles and objects of the present invention are concerned with the provision of an improved magnetron beam switching tube having an improved magnet construction which reduces stray magnetic leakage to a minimum.

In brief, a magnetron-type electron tube embodying the invention includes in a suitable envelope, an electrode assembly including a central longitudinally elongated cathode electrode surrounded by groups of longitudinally elongated electrodes which are adapted to form and receive an electronA beam from the cathode. A magnet assembly, including at least two coaxial cylindrical permament magnets, surrounds the tube envelope and the electrodes contained therein. The axis of the magnet assembly is coaxial with the longitudinal axes of both the envelope and the electrode assembly. The outer magnet of the magnet assembly has a higher coercive force than the inner magnet, and it also has a low reluctance approaching that of air so that it tends to force the magnetic ux of the inner magnet into the tube envelope where it is needed and it by-passes what small amount of stray ux tends to escape from the inner magnet.

The invention is described in greater detail by reference to the drawing wherein:

FIG. 1 is a perspective view of a tube embodying the invention;

FIG. 2 is an elevational view, partly in section, of a tube embodying a modication of the invention; and

FIG. 3 is an elevational view, partly in section, of another modication of the invention.

The principles of the invention are applicable to magnetron tubes and, particularly, to a magnetron beam switching tube, Type 6700. This type of tube is shown in FIG. 1 as tube 10 and includes, brietly, an envelope 12 which contains an electrode assembly including a central longitudinally elongated cathode 14 and ten groups of electrodes spaced radially equidistantly from the cathode and surrounding the cathode and parallel to each other and to the cathode. Each group of electrodes includes a generally U-shaped elongated spade electrode 16 and a generally L-shaped target electrode 18 positioned so that each target occupies the space between adjacent spade electrodes. Each spade electrode serves to form and hold an electron beam on its associated target electrode. A generally rod-like switching electrode 20 is also included in each group of electrodes and is positioned between one edge of each target electrode and the adjacent spade electrode. 'Ihe switching electrodes are known as switching grids.

An open-ended cylindrical permanent magnet 22 is provided surrounding the tube envelope and coaxial therewith. The magnet is secured to the tube envelope in any suitable manner, for example, by means of a layer 24 of a suitable adhesive material such as a synthetic resin. The magnet 22 provides an axial magnetic field which is utilized in conjunction with electric fields within the tube to form and switch an electron beam from the cathode to each of the groups of electrodes. The direction in which the beam switches, that is, clockwise or counterclockwise, is always the same and is determined by the orientation of the electric and magnetic fields.

Briey, in operation of the tube 10, electrons emitted by the cathode are retained at/the cathode if each of the spades, targets and switching grids carries its normal operating electrical potential. When a spade or switching grid experiences a suitable lowering of its potential, an electron beam is formed and directed to the corresponding target electrode. Ordinarily with a cylindrical magnet alone, as shown in FIG. 2 and without a suitable shielding arrangement, useful magnetic ux ows out of the magnet and into the tube, but some ux also flows out of the magnet and away from the tube as stray dux. Thus, if two such tubes are operated in close proximity, the stray ux from one adversely aects the longitudinal tield within the envelope of the other.

According to the invention, the problem of stray magnetic ux which would be generated by magnet 22 is substantially eliminated by the provision of a second magnet 30 coaxial with and surrounding the magnet 22 but insulated therefrom. The magnet 30 is secured to magnet 22 in any suitable fashion, for example, by means of a resin adhesive layer 31. 'I'he outer magnet 30 is of higher coercive force than the first magnet and has a low permeability preferably approaching that of air. The outer magnet serves to force more of the flux of magnet 22 into the tube where it becomes useful tlux and, in addition, any stray ux is substantially completely absorbed by the outer magnet 30.

In the modification of the invention shown in FIG. 2, the single auxiliary external magnet is provided as two rings 30 spaced apart adjacent to and surrounding the ends of the inner magnet 22. The rings 30 are suitably insulated from the magnet 22 by adhesive layers 31'.

If desired, a metallic shield may be employed with any type of tube employing a double magnet construction according to the invention. As shown in FIG. 3, such a shield 32 is in the form of a pipe surrounding and enclosing the tube and the magnets 22 and 30. The shield 32 is preferably of low reluctance material which does not retain magnetism, for example, low carbon steel.

What is claimed is:

l. A magnetron beam switching' tube which operates with crossed electric and magnetic elds with the magnetic tield being longitudinally oriented within the tube, the tube including an envelope, and an electrode cage mounted within said envelope, said electrode cage including a central cathode electrode and a plurality of groups of electrodes surrounding said cathode and adapted to receive an electron beam from said cathode, and rst and second cylindrical magnets .surrounding said envelope, said second magnet surrounding the irst magnet and re 3 ducing the leakage of magnetic ux from said irst magnet and providing a longitudinal magnetic field therein.

2. The tube defined in claim l wherein said first and second magnets are arranged coaxially with one inside the other, the outer magnet having high coercive force and low permeability.

3. The tube delned in claim 1 wherein said first and second magnets are arranged coaxially with one inside the other, the outer magnet having high coercive force and low permeability approaching the permeability of air.

4. The tube dened in claim l wherein said first and second magnets are arranged coaxially with one inside the other, the outer magnet having higher coercive force than the inner magnet and low permeability.

5. The tube dened in claim 1 and including a cylindrical shield surrounding the magnets and coaxial therewith.

6. A magnetron beam switching tube including an .en-i

velope and an electrode cage mounted within said envelope, said electrode cage including a central cathode electrode and a plurality of groups of electrodes surrounding said cathode and adapted to receive an electron beam from said cathode, and a coaxial assembly of inner and outer permanent magnet means surrounding said electrode cage and providing a longitudinal magnetic eld within said electrode cage, said outer magnet means substantially preventing the leakage of magnetic ux from said inner magnetic means away from said electrode cage while causing magnetic ux to ow into said electrode cage.

References Cited in the file of this patent UNITED STATES PATENTS 2,465,342 Arditi Mar. 29, 1949 2,721,955 Fan et al. Oct. 25, 1955 2,849,645 Haddad Aug. 26, 1958 2,876,376 Rienks Mar. 3, 1959 UNITED STATES PATENT OFFICE :E`111111f;n111 0F CORRECTION Patent No. 3,032,678

May 1, 1962 David Glaser It is hereby certified that error appears in the above numbered pat-g ent requiring correction and that the seid Letters Patent should read as corrected below.

Column 2, line 7l, after "envelope" insert and providing a longitudinal magnetic field therein column 3,

field therein".

signed and sealed this 16th day of october 1962.

(SEAL) Attest:

ERNEST W. SWIDER` Atteeting Officer DAVID L. LADD Commissioner of Patents 

